The following sections discuss a number of topics that involve
multi-host connections, namely, server load-balancing, failover,
and replication.

Developers should know the following things about multi-host
connections that are managed through Connector/J:

Each multi-host connection is a wrapper of the underlying
physical connections.

Each of the underlying physical connections has its own
session. Sessions cannot be tracked, shared, or copied,
given the MySQL architecture.

Every switch between physical connections means a switch
between sessions.

Within a transaction boundary, there are no switches between
physical connections. Beyond a transaction boundary, there
is no guarantee that a switch does not occur.

Note

If an application reuses session-scope data (for example,
variables, SSPs) beyond a transaction boundary, failures
are possible, as a switch between the physical connections
(which is also a switch between sessions) might occur.
Therefore, the application should re-prepare the session
data and also restart the last transaction in case of an
exception, or it should re-prepare session data for each
new transaction if it does not want to deal with exception
handling.